The purpose of the proposed project is to determine biochemical and genetic mechanisms responsible for regulating the orderly expression of genes during fungal development. The organism to be studied is the genetically well characterized Ascomycete, Aspergillus nidulans. A. nidulans reproduces asexually by forming multi-cellular conidiophores and uninucleate conidia. It has been shown that this process is characterized by the accumulation of numerous cell-specific messenger RNAs. Many recombinant DNA clones containing genes that are regulated during conidiogenesis have been obtained. In addition, a series of developmental mutants have been isolated, having properties that suggest they represent lesions in genetic loci involved in regulating gene expression during conidiophore development. The currently available recombinant DNA clones, Aspergillus transformation system and developmental mutants will be used to attempt to identify genetic regulatory elements and to begin to determine how they function and how they are arranged into control networks. Three sets of experiments with related objectives are planned of the proposed funding period. The objectives of these experiments are 1) to determine the mechanisms controlling expression of genes within a large cluster of developmentally regulated genes, 2) to isolate and characterize three genetic loci having properties that indicate they are developmental regulatory elements and 3) to isolate and characterize two developmentally regulated genes having related and well defined physiological roles in spore differentiation. This work will provide important new information concerning the reproductive molecular biology and genetics of a group of organisms that includes many serious animal and plant pathogens and may suggest methods and approaches for controlling their spread. In addition, the result will be relevant to the broader question of how multicellular organisms coordinate the expression of the many genes contibuting to the phenotypes of differentiated cells.